Generally, electrofusion fittings comprise one or more tubular openings adapted to receive a pipe to be connected to the fitting. The tubular opening has an electrofusion element embedded in the internal surface of the opening that lies against the pipe when the pipe is inserted in the fitting. The electrofusion element frequently comprises a coil of resistance wire. The coil generally begins well inside the mouth of the opening and ends before the end of the fully-inserted pipe. Usually a rib or the like forms a stop in the opening, determining when the pipe is fully inserted once its end abuts the stop. This ensures that the element is fully covered on both sides, by the pipe, on the one hand, and by the fitting on the other. When the electrofusion element is energised, the plastics material of the pipe and fitting adjacent the electrofusion element melts and fuses. Both the pipe and the fitting are sufficiently thick, and being made of plastics material which is a poor conductor of heat, so that the liquefied plastics does not penetrate out through the fitting, or in through the wall of the pipe. Moreover, because there is overlap of fitting at one end of the coil and pipe at the other, the melting does not penetrate to the end of the fitting or to the end of the pipe. So the melting is contained. Moreover, the plastics expands somewhat on melting, so that there is an increase in pressure in the melting zone that aids fusion. An aperture is sometimes provided in the fitting communicating with the bore thereof in the region of the coil, so that melted plastics is exuded through the aperture to indicate melting and probable completion of the weld.
When joints are made, they are not always successful. A successful joint is one where the fitting and pipe are fused in a ring around the fluid passage of the pipe, and over a considerable length of the pipe so that a leakage or fracture path, if one develops, has to penetrate a long distance. This applies both to a tubular fitting and to a saddle fitting. There can be a number of reasons why a joint is not successful, and sometimes the fact that it is unsuccessful is not immediately apparent. Of course, mating surfaces of the fitting and pipe in the region of the electrofusion element have to be clean and “unskinned” (that is, having no oxide layer formed on the surface), otherwise proper fusion, which involves surface mixing between the two parts, may be inhibited. Also, the mating surfaces must lie close to one another over the entire fusion range, otherwise they may be too far apart for the liquefied plastics to meet over a long length of the complete circumference of the joint. Finally, there should be no relative movement between the pipe and fitting during the fusion process. If movement occurs, this can lead to the pipe not covering the fusion zone and thus weakening the joint.
Measures already exist to overcome these problems. For example, it is normal to scrape pipes to remove oxide layers, or provide them with a plastics surface skin that is peeled off prior to fusion to expose virgin plastics material. The present invention is not concerned with this aspect, however. It is also known to clamp pipes and fittings together prior to fusion, so that the possibility of movement is avoided. It is an object of the present invention to improve on this arrangement. In particular, it is desirable to provide a fitting where angular or axial misalignment between a pipeline and fitting is minimised, since this is another reason for some unsuccessful joints. Given that movements of the pipe at critical times, or occasions when the pipe is not sufficiently central, are rare, pipe failures are also rare. However, this means that users in the field tend to be complacent about employing the cumbersome clamping arrangements hitherto available. Thus an improved arrangement would be desirable.